1. Field of the Invention
This invention relates to a conductive contact structure for two conductors in which the planar portion of an electrode plate relatively large in area on which for instance flat package type semiconductor elements are fixedly mounted is brought into contact with the planar portion of a conductor under pressure which also serves as a cooling element so that the electrode plate and the conductor are conductive to each other; in which the pressure contact area is improved in electrical conductivity and in thermal conductivity; i.e., heat radiation.
2. Discussion of the Related Art
A conventional conductive contact structure for two conductors will be described with reference to FIG. 5, a side view, which has been proposed by the present, Applicant (under Japanese Patent Application (OPI) No. 230670/1990 (the term "OPI" as used herein means an "unexamined application")). In FIG. 5, reference numeral 50 designates a cooling fin; 54, an upper electrode; 55, a lower electrode; 56, a semiconductor element which is conductively mounted on the lower electrode 55; and 57, a lead wire connected between the upper electrode 54 and the semiconductor element 56. The cooling fin 50 is one of the two conductors, and the lower electrode 55 is the other. The two conductors are brought into contact with each other being pressurized by a force F. More specifically, in this operation, the lower electrode 55 is deformed in such a manner that its middle portion contacts the surface of the cooling fin 50 as much as a width We which is slightly larger than the lateral width of the lower surface of the upper electrode 54, while its both side portions are elastically deformed being slightly raised above the surface of the cooling fin 50. In this case, in order to ensure the electrical conductivity and the thermal conductivity, or heat radiation of the pressure contact surface with a relatively small force F, the following method is employed: A plurality of grooves are formed in the lower surface of the lower electrode 55 in the range of the width We in such a manner that they are extended perpendicular to the surface of the drawing and in parallel with one another. And a grease-like insulating material 9 high in thermal conductivity is applied between the lower surface of the lower electrode 55 and the upper surface of the cooling fin 50. Instead of the method in which the grooves 53 are formed in the middle of the lower surface of the lower electrode 55, the following methods may be employed. In one of the methods, the surface roughness of the lower surface of the lower electrode is set to about 10 to 100 .mu.m. In the other method, the above-described two methods are employed in combination; that is, the grooves are formed in the middle of the lower surface of the lower electrode, and the surface roughness of the lower surface of the lower electrode is adjusted.
The conventional conductive contact structure shown in FIG. 5 suffers from the following difficulties: (1) Machining the lower electrode to form the grooves 53 is rather troublesome, taking time and labor. (2) The electrical conduction is somewhat low in reliability. In other words, in order to eliminate the difficulty that the electrical conduction is low in reliability, it is necessary to increase the pressurizing force to some extent.